1. Field of the Invention
The present invention relates to a method and the related plant for rendering inert a loose mixture containing a hardenable resin with an organic solvent and solid inert materials.
2. Description of the Related Art
There are numerous industrial applications which make use of mixtures containing hardenable resins dissolved in organic solvents.
One industrial application which envisages the use of hardenable resins relates to the manufacture of conglomerate stone articles. An example consists in the articles which are produced using the so-called “Bretonstone technology” where an initial mix, formed of particles of stone, ceramic or stone-like aggregate with a controlled particle size, a fine filler and a binder, is deposited on a temporary support, subjected to a compaction step by means of vacuum vibrocompression and then transferred for the hardening step which is performed in the presence of a catalyst when the binder consists of a resin. For a description of the aforementioned Bretonstone technology reference may be made, for example, to the following patents: IT-A-1,181,570 relating to preparation of the initial mix, EP-A-0,786,325 and 1,027,205 relating to the use of organic binders.
The binder products used are preferably polyester resins, diluted with a reactive monomer such as styrene, which participates actively in the catalytic hardening step.
For this reason the initial mix usually also contains the catalyst and, where necessary, a catalysis accelerator/initiator.
It must be pointed out firstly that polyester resin is a synthesis product derived from petroleum, the problems of which as regards its impact on the environment are well-known.
Moreover, the presence in the mix of the styrene monomer as a reactive solvent of the polyester resin gives rise to various environmental problems associated with its toxic nature and the danger of explosion because of its high volatility: sophisticated and costly plants for capturing and eliminating the styrene vapours are in fact necessary in order to comply with increasingly stringent regulations.
Even though individually the resin and solvent are problematic from an environmental point of view because of the risk of pollution, in the case of Bretonstone technology, the final product—in other words the conglomerate stone sheets or blocks—is totally inert since the resin is catalysed and hardened in a solid non-reactive state.
Management of the initial mix, however, is problematic: in fact, when plants which perform all the stages of production of the articles are used, during relatively long stoppages of the machines (for example from a previous evening to the following morning), the disadvantage is that a certain quantity of initial mix remains unused and, since it cannot be compacted and converted into the final product, must be disposed of. The uncompacted mix is a loose and soft granular mass.
In this latter case, however, the polyester resin dissolved in the styrene within the mix is in the active state and therefore it is of a potentially polluting nature.
A similar problem arises with the remainder of mix resulting from cleaning of the production line and in particular the equipment for preparing and distributing the mix onto the forming moulds; it may also be in the form of a granular and loose mass.
Is therefore required to dispose of the unused mix in special waste tips which are equipped to deal with the so-called toxic waste, with obvious management and disposal costs.